Can offline tiles be loaded

[kunalkhosla93]

Hi,

Is it possible to load offline tiles from a directory using this? if so how?

[raptorswing]

Hi. Sorry for the slow response. It is possible, but might require a bit of effort. The code supports different "Tile Source" implementations. These can have their own implementations for loading tiles (e.g. HTTP requests, drawing on the fly, or loading from disk). There isn't one built-in for loading from disk, but the base class that they all inherit from does have the ability to store downloaded/rendered tiles to a disk cache and then load from there instead of hitting the network or rendering the tiles again.

See, for example, parts of the caching implementation in MapTileSource:

MapGraphics/MapGraphics/MapTileSource.cpp

Lines 169 to 219 in 0cf9af2

	QImage *MapTileSource::fromDiskCache(const QString &cacheID)
	{
	//Figure out x,y,z based on the cacheID
	quint32 x,y,z;
	if (!MapTileSource::cacheID2xyz(cacheID,&x,&y,&z))
	return 0;
	//See if we've got it in the cache
	const QString path = this->getDiskCacheFile(x,y,z);
	QFile fp(path);
	if (!fp.exists())
	return 0;
	//Figure out when the tile we're loading from cache was supposed to expire
	QDateTime expireTime = this->getTileExpirationTime(cacheID);
	//If the cached tile is older than we would like, throw it out
	if (QDateTime::currentDateTimeUtc().secsTo(expireTime) <= 0)
	{
	if (!QFile::remove(path))
	qWarning() << "Failed to remove old cache file" << path;
	return 0;
	}
	if (!fp.open(QFile::ReadOnly))
	{
	qWarning() << "Failed to open" << QFileInfo(fp.fileName()).baseName() << "from cache";
	return 0;
	}
	QByteArray data;
	quint64 counter = 0;
	while (data.length() < fp.size())
	{
	data += fp.read(20480);
	if (++counter >= MAX_DISK_CACHE_READ_ATTEMPTS)
	{
	qWarning() << "Reading cache file" << fp.fileName() << "took too long. Aborting.";
	return 0;
	}
	}
	QImage * image = new QImage();
	if (!image->loadFromData(data))
	{
	delete image;
	return 0;
	}
	return image;
	}

You could conceivably implement a tile source that reuses this caching functionality, or maybe do something else. In either case, you'll probably want to implement a child class of MapTileSource.